@Man Eating Duck - IIRC there is no code in this plugin that manipulates the creator. It calls stock calibre code for updating the metadata like that. So I believe you will need to point that one towards Kovid if he doesn't spot it - it only happens when you tick the "Update metadata" box right?

Re the remove non dc:metadata option. Yeah I agree it isn't ideal how it works currently, but it isn't trivial to change which is why it was on the bottom of the priority list. This plugin basically does the following:
- unzips the epub
- applies all modifications except update metadata
- rezips the epub
- calls calibre code to update metadata that requires a zip

So in order to move the non dc check, the epub has to be unzipped and rezipped a second time, which isn't "ideal". But if it is the only way to make the function useful then so be it, will take a look sometime since other features/functions of this plugin seem to have stabilised.